By Casey Cooper-Fiske

William Shakespeare’s four folios published more than 300 years ago are to go on auction in London.

They are expected to fetch between £3.5 million ($A7.3 million) and £4.5 million ($A9.4 million).

The books, which compile Shakespeare’s plays, will go on sale at Sotheby’s on May 23, a month after the Bard’s birthday on April 23.

Experts say the first folio, which contains 36 of Shakespeare’s plays, is “the most significant publication in the history of English literature”, adding that without it up to half of the writer’s plays would have been lost, including Macbeth, Twelfth Night and Julius Caesar.

Alongside the King James Bible, the auctioneers say the book has had “the greatest impact on the development of the English language itself”.

The first book’s initial print run is thought to have been around 750 copies, which prompted the release of the subsequent volumes to keep up with demand, with the books published between 1623 and 1685.

The folios were put together by John Heminges and Henry Condell, who were close friends of Shakespeare as actors and shareholders in the King’s Men, the acting company to which Shakespeare belonged for most of his career.

Shakespeare even left the pair money for a mourning ring in his will.

The earliest recorded purchase of the first folio was in December 1623, when Edward Dering bought two copies for £2.

The third folio is the rarest of the books, with the Shakespeare Census listing 182 copies still in existence, just over half of the number of surviving second and the fourth folios.

It is believed the third book’s rarity is because a proportion of stock was destroyed in the Great Fire of London in 1666.

Born in 1564, Shakespeare is considered one of Britain’s greatest writers, with his best known plays including Romeo And Juliet, Macbeth and Hamlet. He died on his birthday in 1616 aged 52.

Was he? Wasn’t he? The Bard is back in the dock